There are various types of bevel and hypoid gears. For example, circular-arc toothed bevel gears are fabricated in the single indexing process (also called intermitted indexing process, single indexing process or face milling). The single indexing process is shown schematically in FIG. 1. The blades 21 of a cutter head 20 execute a circular movement while one slot of the bevel gear 11 to be produced is fabricated. In order to fabricate further tooth gaps, the cutter head 20 is retracted and the work piece 11 is turned through a pitch angle. The stepwise further turning (here in the anticlockwise direction) is indicated in FIG. 1 by the arrows A, B, C (called indexing rotation). Thus, one tooth gap 22 is always fabricated in one operation.
Epicycloidal, in particular expanded epicycloidal (also called lengthened epicycloidal) toothed bevel gears on the other hand are fabricated by a continuous indexing process (also known as continuous milling, continuous indexing process or face hobbing). In this continuous indexing process both the cutter head and the work piece rotate in a movement sequence matched temporally to one another. The indexing is therefore accomplished continuously and slots and the corresponding teeth are produced quasi simultaneously.
It is known that a ring gear can be produced not only by hob milling but also by plunging (also called insertion). In this case, the tool is advanced into the work piece. A forming process or also of a FORMATE-gearing (FORMATE is a trademark of The Gleason Works, Rochester, N.Y., USA) is discussed. This procedure saves time in the fabrication of the ring gear. As no generating rolling movement takes place, the tool profile is imaged in the ring gear slot. The ring gear thus fabricated then has the profile of the tool, i.e., the profile curvature of the tooth flanks is obtained directly from the tool profile shape of the first tool. The corresponding conjugated bevel gear pinion of a bevel gear pair can then however be manufactured in a modified rolling process, so that the rolled pinion and plunged ring gear can run or mesh correctly with one another. Details on this can be obtained, for example, from the book “Kegelräder; Grundlagen, Anwendungen” (Bevel gears; principles, applications”), by J. Klingelnberg, Springer Verlag, 2008, pages 16-17.
Known from U.S. Pat. No. 1,982,036 is a process for producing a plunged ring gear and a matching rolled pinion, where both bevel gears in this example have tapered teeth. Details of the process mentioned can be deduced from U.S. Pat. Nos. 2,105,104 and 2,310,484. These patents are concerned with the manufacture of arc-teethed or spiral-teethed bevel gears.
During plunging, the tool can be inserted to a predetermined depth in the work piece before the machining removal of material is ended. The plunging is usually accomplished by feeding the tool linearly relative to the work piece, e.g., by a linear movement of a carriage parallel to the tool axis. It is obvious that with increasing plunging, the so-called active cutting length that performs chip-removing machining work increases. This has the consequence that the forces that occur and the loading of the axes of the machine increase. Non-uniform tool and machine loadings can therefore occur during the plunging. In addition, the NC control of the machine is under greater stress because it attempts to compensate for any vibrations that are produced.
The occurrence of non-uniform tool loadings is described, for example, in EP Patent No. 0850120 B1. EP 0850120 B1, however, is primarily concerned with providing a solution that should allow the chip load of the so-called secondary cutting edge of a blade of the tool to be reduced. According to EP 0850120 B1, a special approach for advancing the tool to a predetermined depth in the work piece is described. A feed path that is composed of two vector components is predefined. The first vector component runs in the direction of the tool axis, as in conventional plunging and the second vector component runs in the direction of the surface width of the work piece, i.e., along the tooth gap.
It is known from International Patent Application Publication No. WO 97/31746 that a cup-shaped tool can be used for chip-removing machining treatment of a work piece such that the plunging is already beginning while the work piece still executes an indexing rotation. The object of this patent application was to make the process duration shorter.